Diffuse reflectance spectra of ten crystalline chromate salts have been measured. Three main alterations can be observed when comparing the reflectance spectra with the spectrum of the chromate ion in solution: (1) the increase in the intensity of the 23,000 cm-1 band in crystalline chromates; (2) the shift of the 36,000 cm-1 band towards lower energies with the increasing polarizing effect of the cations, and (3) the appearance of new low-energy bands in case of highly covalent metal-chromate bonds. The interpretation of the first two phenomena confirm the assignment of the spectral bands obtained in the ab initio calculations of Hillier and Saunders . The first band is very likely symmetry-forbidden, but becoming allowed in the solid salts. A crystal-field-like model is suggested for the explanation of the red shift of the 36,000 cm-1 band which leads to the conclusion that it corresponds to the t1 → t2 transition. The new bands appearing in the spectra of silver, thallium and lead chromate are assigned to cation-anion charge transfer.
|Number of pages||6|
|Journal||Spectrochimica Acta Part A: Molecular Spectroscopy|
|Publication status||Published - 1978|
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